Cross flow fans are used in blowers of indoor units of air conditioning apparatus. A cross flow fan is equipped with an impeller that has a circular plate and plural blades disposed on the outer periphery of the plate. FIG. 15 shows the cross-sectional shape of a blade of a cross flow fan disclosed in Japanese Utility Model Application Laid-open No. S57-157788 and Japanese Patent Application Laid-open No. H2-169896. As shown in FIG. 15, the cross-sectional shape of a blade 500 is a crescent shape that is bilaterally symmetrical about a centerline (the long dashed short dashed line), is thick in the center, and is thin at both ends. In this kind of blade whose cross section has a crescent shape, the radii of an outer peripheral side arc Ro and an inner peripheral side arc Ri of the blade are equal, a convex surface side arc Rs and a concave surface side arc Rp of the blade are each configured by single arcs, and Rp>Rs. However, in a case where a blade whose cross section has a crescent shape is employed as the blades of a cross flow fan, as shown in FIG. 16, in flow paths between the plural blades, a flow path diameter Di on the inner peripheral side of the blades is decreased to a flow path diameter Do′ on the outer peripheral side of the blades, and the change in the flow path width from the inner peripheral side to the outer peripheral side of the blades is great, so the change in the air flow speed becomes greater. Specifically, as shown in FIG. 17, the flow path width on the outer peripheral side becomes 24.3% narrower, and flow velocities become greater on the outlet side. Thus, air flow turbulence becomes greater, it becomes difficult for the air flows to flow along the flow paths, and flow separation occurs on the outlet side suction surfaces. As a result, power loss caused by the fan increases.
Furthermore, in a cross flow fan disclosed in Japanese Patent No. 4,583,095, in order to suppress noise and an increase in motor input caused by flow separation at blade surfaces at times of high pressure loss, there is disclosed a cross flow fan blade shape which, in a case where the chord length is equally divided, forms a streamline that is asymmetrical with respect to the division line, with the ratio of a fan inner peripheral side cross-sectional area Sa to a fan outer peripheral side cross-sectional area Sb being equal to 1.3 to 1.6 (Sa/Sb=1.3 to 1.6), the ratio of a dimension Rb of a fan outer peripheral side distal end R to a dimension Ra of a fan inner peripheral side distal end R being equal to 0.1 to 0.8 (Rb/Ra=0.1 to 0.8), and the blade cross-sectional thickness reaching a maximum in the center of the chord length. However, in a blade with this shape, the flow path width between adjacent blades does not gradually decrease from the inner peripheral side toward the outer peripheral side, and there are sections where the change in air flow speed is not stable.